Heather C. Brenhouse, Ph.D. - US grants

DESCRIPTION (provided by applicant): This project aims to elucidate the interactive neurobiological and immunological effects of early life stress (ELS) in an animal model. The overarching goal of these studies is to prevent behavioral deficits later in life by intervening during an early and critical period. The results could potentially translate to techniques for identifying which ELS-exposed individuals are vulnerable to psychiatric disorders, and which might benefit from prophylactic therapies. We have exciting preliminary data in rats that shows ELS leads to the loss of parvalbumin (PVB)- expressing interneurons in the prefrontal cortex (PFC) and cognitive deficits during adolescence, which are key features of several psychiatric disorders. Moreover, these effects of ELS are preventable with pre-adolescent inhibition of neuroinflammatory activity. Neuroinflammatory damage occurs largely through the actions of cytokines and glutamate. We recently showed that both circulating cytokines and glutamatergic receptors are altered in ELS-exposed adolescents. Therefore, the proposed experiments will determine how ELS derails the healthy developmental trajectory of immune signals and glutamatergic receptors in the PFC to cause deleterious changes later in life. These studies accomplish two specific aims. First, we will examine potential immunological biomarkers that could predict later effects of ELS. We will use a highly sensitive assay to measure circulating cytokines in young rats exposed to varied time-courses of ELS. Collaboration with an expert on immunological measurements will allow us to assay multiple cytokines from small blood samples. The comparison of effects from different ELS time-courses will also help clarify existing inconsistencies in the literature. We will assess the predictive value of circulating cytokines by correlating early levels with later changes in PVB and behavior. Second, we will localize a mechanistic cause of cellular and behavioral dysfunction by investigating the role of glutamatergic receptors in ELS effects. In one experiment, we will target the NMDA receptor subunit NR2A, which we have shown is over-expressed in ELS adolescents. During the pre-adolescent window, we will microinject the cell-permeable peptide TAT2A into the PFC in order to uncouple NR2A from the intracellular machinery. We will determine whether blocking the effects of NR2A overexpression will help protect ELS-exposed animals from PVB loss and behavioral dysfunction. In another experiment, we will investigate whether ELS-induced neuroinflammation produces the same deleterious changes in AMPA receptors as other inflammatory events have been shown to produce. Taken together, we will test the following hypothesis: ELS increases inflammatory signaling that interacts with altered PFC glutamatergic receptor development to cause behavioral and neural dysfunction in adolescence.

This project aims to elucidate developmental neurocircuitry effects of early life stress (ELS) in an animal model. Growing clinical evidence suggests that many ELS-attributable mental illnesses manifest in adolescence after an apparent latent period, and are unresponsive to traditional therapies. Our lab and others have further shown that these ELS-attributable effects follow a different time-course in males and females. Therefore, there is a need to understand aberrant developmental mechanisms that likely require targeted intervention and treatments in ELS-exposed individuals. Our recent studies revealed that ELS causes overexpression of the glutamatergic NMDA receptor subunit NR2A in the prefrontal cortex (PFC) of male adolescents. Importantly, targeted manipulation of NR2A protected ELS-exposed males from behavioral deficits such as increased anxiety-like behavior. Our preliminary data further suggests that NMDAR changes and increased anxiety appear earlier in development in ELS-exposed females, compared to ELS-exposed males. Understanding the developmental trajectory between ELS exposure and altered PFC receptivity is necessary to effectively intervene with preventative treatments. PFC receptivity is largely driven by glutamate activity in the PFC from limbic inputs, therefore the impact of ELS on corticolimbic connectivity requires delineation. The proposed project aims to target developmental origins of PFC dysfunction in ELS-exposed males and females. The central hypothesis is that ELS alters development of PFC innervation and glutamate receptivity in a sex-specific manner. These studies will first reveal sex-specific ELS effects on corticolimbic connectivity (Aim 1) and innervation (Aim 2) throughout development. Effects of ELS on PFC connectivity will provide translational data that can be juxtaposed with recent clinical findings in ELS-exposed boys and girls and will elucidate a likely mechanism behind how ELS leads to receptor alterations later in life. Aim 3 will investigate the developmental trajectory of post-synaptic NMDA receptor subunit changes after ELS. We will also determine critical periods when deactivating PFC NR2A function can prevent ELS-induced behavioral deficits later in life. Since recent evidence suggests that females show earlier ELS-attributable changes than males, we will determine whether females require an earlier intervention than males to prevent ELS-induced behavioral dysfunction. Together, these studies will fill critical gaps in knowledge about the developmental and sex-specific nature of ELS effects on PFC circuitry and are expected to have significant impact on the development of specific targets for prevention in ELS-exposed populations.

Project Summary Exposure to early life adversity (ELA) confers significant risk for psychiatric disorders that are often unresponsive to traditional treatments. Importantly, most ELA-attributable psychopathologies involve heightened responsivity to potential threats, yet our mechanistic understanding of this susceptibility remains incipient due to insufficient knowledge about how experience, sex, and age interact to affect the development of threat-responsive circuits. Thus, this project aims to identify causal mechanisms initiated by ELA that drive heightened corticolimbic connectivity and enhanced threat responsivity. Our long-term goal is to enable translation of these findings into individualized intervention strategies. Our groups have shown that ELA leads to development of heightened anatomical (innervation) and functional (BOLD; local field potential) connectivity between the basolateral amygdala (BLA) and the prefrontal cortex (PFC) in early adolescence, as well as higher anxiety-like behaviors. Several of these effects emerged earlier in females than in males, and our preliminary findings suggest that pubertal sex hormones may impact the sex-specific development of BLA-PFC connectivity following ELA. We will therefore test the central hypothesis that ELA disruption of peri-pubertal BLA activity and hormonal signaling accelerate development of BLA-PFC connectivity in a sex-specific manner, altering PFC-regulated threat responsivity across the lifespan. Our studies will first use electrophysiological and chemogenetic approaches to reveal sex-specific critical periods of BLA activity that drive hyper-connectivity with the PFC (Aim 1), enhanced responsivity to potential threat (Aim 1), and glutamate receptivity in the PFC (Aim 2). Aim 3 will investigate a peri-pubertal neuroendocrine mechanism using RNA silencing to determine whether estrogen receptor signaling in the BLA drives hyper-connectivity to the PFC, glutamate transmission in the PFC, and heightened threat responsivity. Together, these studies will fill critical gaps in knowledge about the developmental and sex-specific nature of ELA effects on BLA-PFC circuitry and are expected to have significant impact on the development of specific targets for prevention in ELA-exposed populations.